Stretch wrap films

ABSTRACT

A stretchable wrap film comprising a polymer blend comprising (percent by weight): I) 50 to 90% of an ethylene polymer composition comprising a recurring unit derived from an ester selected from (1) ethylenically unsaturated organic monomer of esters of unsaturated C 3 -C 20  monocarboxylic acids and C 1 , to C 24  monovalent aliphatic or alicyclic alcohols, and (2) vinyl esters of saturated C 2 -C 18  carboxylic acids, wherein the ester content ranging from 2.5 to 8 wt % based on the total weight of the final ethylene polymer composition; the ethylene polymer composition having a density ranging from 0.920 to 0.94 g/mL; and II) 10 to 50% of an ethylene-based polymer component having a density ranging from 0.9 to 0.930 g/mL and a melt flow rate up to 4 g/10 min. The stretchable wrap film has a ratio between the value of MD tear resistance and the value of TD tear resistance over 0.3 and a value of MD tensile strength at 30% ranging between 6.5 to 15 N. The stretchable film is suited for use as stretch, cling wraps in various bundling, packaging and wrapping operations.

The present invention relates to a container packaging made ofstretchable wrap films that have good mechanical and chemical-physicalproperties. More particularly, it relates to stretchable cold-shrinkablewrap films made of polyolefin materials comprising a blend of lowdensity ethylene polymers and minor amounts of linear polyethylene.

Stretchable films that self-seal when portions are overlapped are knownas “cling” films. Stretch, cling films, which are most often multilayerfilms, have found utility in a wide variety of applications where it isdesirable to securely hold and/or wrap an article or group of articles.The stretchable films are suited for use as stretch, cling wraps invarious bundling, packaging and wrapping operations, such as stretchwrapping, stretch bundling and tension winding, to wrap or hold a smallarticle or a big article.

One application of particular, but not limiting, interest to the presentinvention is in the bundling of an article or a plurality of identicalor different articles of widely varying types to form a unitary pack. Animportant subset of the said bundling applications is in the containmentand unitizing of pallet loads.

Unitary packs allow articles to be assembled in stable units and inuniform shapes, thereby enabling their transportation to be rationalizedand consequently made more economical but also preserve articlecleanliness. The need of a unitary pack is therefore especially forshipping, transporting and storage and accounting purposes, for examplefrom the manufacturer to a retail outlet.

Nowadays, for wrapping and bundling articles, thermoplastic films havelong been used in lieu of the conventional cardboard boxes. The use ofstretchable films in the field of bundling of industrial and retailgoods constitutes an application of significant commercial importance.

All thermoplastic polymers or copolymers, in the form of stretchablefilms, having a sufficient tear resistance can be employed for packagingand bundling applications. Nevertheless, the polyolefins and, moreparticularly, polyethylene, such as linear low-density polyethylene(LLDPE), or polypropylene, alone or even blended with copolymers ofethylene and propylene and an olefinically unsaturated monomer such asvinyl acetate, are those that are most frequently used industrially. Theconventional films are suited for wrapping groups of articles, the finalwrapping over the groups of articles usually consists of a film/sheet ofheat-shrink material.

Bundling applications are techniques which entail enveloping thetotality of the articles to be packaged with a shrinkable wrapping clingfilm that is stretched tightly around an article or plurality ofarticles. In such applications, it is essential that the films havecling properties in the stretched state. The film is then shrunk byexposing the assembly to sufficient heat to cause shrinking of film andintimate contact between the film and article(s). The heat that inducesshrinkage can be provided by conventional heat sources, such as heatedair, infrared radiation, hot water, hot oil combustion flames, or thelike. For example, the entire assembly is transferred through an oven ata temperature that permits the thermoplastic resin constituting the filmto soften, thus relieving internal stresses. Upon exiting the oven,rapid cooling ensures that the film shrinks tightly and sealedly aroundthe goods contained therein. Thus, a highly homogeneous bundle orunitary pack is produced in which the film functions as a skin in tightcontact with the surface of the packaged goods.

The high cost of the heat shrink film, however, makes the wrapping veryexpensive, not to mention that in some cases and for some types ofproducts, the wrapping lines may, also, be very expensive for themanufacturer because they have numerous operating units, such as productcollating units (especially in the case of continuous lines), and filmfeed and heating units, all of which require a high number of controldevices and accessory parts. Another limiting factor on the use of heatshrink films and lines of this kind is the fact that some productscannot be heated beyond certain limits, which means that heat shrinkwrapping solutions are not feasible.

As mentioned above, prior art films comprising a blend of linearlow-density polyethylene (LLDPE) and olefinically unsaturatedmonomer-ethylene copolymers are already known also for use in bundlingand packaging in general.

For example, European patent application 377,121 disclosesheat-shrinkage films having a layer made from a blend of 10-50 wt % oflow density polyethylene (LDPE) and 50-90 wt % of ethylene-1-olefincopolymer having low density. However, it is well known from industrythat such type of blends has improved processability and opticalproperties but has unbalanced mechanical properties.

U.S. Pat. No. 4,551,380 discloses heat-shrinkable multi-layer filmswherein the surface layer is a blend of linear low density polyethylene,linear medium density polyethylene and ethylene-vinyl acetate copolymer.

U.S. Pat. No. 5,399,426 discloses a stretch wrap film having at least acore layer made from a polymer blend that consists of about 3 to about16.7 wt % of branched polymer, such as ethylene-vinyl acetatecopolymers, and about 83.3 to about 97 wt % of linear polyethylene, suchas linear low density polyethylene (LLDPE) and ultra linear low densitypolyethylene (ULDPE). The mono- or multilayer film is produced by knownblown film and cast film processes.

The latter films are not suitable to use in bundling applications due totheir poor elastic or unbalanced holding force retention that influencestoughness of packaged items.

Hence, there is a commercial need for a stretchable wrap film that doesnot require heat to be shrunk and having the characteristics requiredfor bundling.

The Applicant has now found a stretchable cold-shrinkable wrap film thatexhibits mechanical, optical and chemical-physical properties that makethe film suitable for use in bundling applications, of an article or aplurality of articles to provide a unitized packaged unit.

Thanks to its improved mechanical and physical properties, the films ofthe present invention are particularly useful to the bundling of groupsof relatively large and, above all, quite heavy products, such as largerolls of carpet, fabric, bottles or the like. In particular, by bundlingtechnique the manufacture of a secondary container packaging materialfor a plurality of articles such as canned food, bottles and cans isalso carried out. The term “secondary container packaging” as generallyunderstood in the industry and as used herein refers to packaging usedin conjunction with primary containers, such as cans or bottles, whichcontain the ultimate product, such as food, beer, water or otherbeverages. Secondary container packaging includes container wraps whichsurround and support the primary containers, and an upwardly extendinghandle.

The present films have a good balance of mechanical properties, inparticular a very high degree of stretchability of the films combineswith the good elastic recovery and high residual strength. The inventedfilms can stretch to wrap the goods but cannot permanently lose theirshape. The elastic recovery allows the films to shrink and the highresidual strength keeps the goods pressed.

The present films also show good holding force retention after packagingitems as well as good impact resistance but also transparency among theoptical properties.

The film of the present invention has also good heat-sealability that isrequired due to the type of packaging technique that can be used.

The film of the present invention has a quite balanced ratio betweenmachine direction tear resistance and transverse direction tearresistance,

The film of the present invention offers the considerable advantage thatnow it can be manufactured a secondary container packing having a handlestructure that is formed as integral part of the secondary containerpacking. Hence, the handle structure is made up of the same type of filmas the remaining part of the container packaging. Therefore, there is noneed of applying a separate handle to the container packaging, thusreducing the overall cost of such a packaging. In addition, thepackaging can entirely be made of polyolefin materials and thusrecycling of the whole packaging is easier because it is no longernecessary to remove the handle from the film.

Another advantage is provided with the film of the present invention asa result of the superior property balance, the film can have asignificantly lower thickness than that of the currently used films inthe same field of packaging. This allows both cost savings and reductionof the environmental impact.

The film of the present invention exhibits another great advantage forthe industry because heat is not required to shrink the film arounditem(s). In fact, after the film is stretched to wrap the item(s), thefilm shrinks around the item(s) without subjecting the film to elevatedtemperatures. Even room temperature allows the film to shrink around theproduct to produce a tight wrapping that closely conforms to the contourof the item(s). This allows to make time and energy savings.

Therefore, the present invention provides a stretchable wrap filmcomprising an olefin polymer blend comprising (percent by weight):

-   I) 50 to 90%, preferably higher than 50 to 90%, more preferably 65    to 80%, of an ethylene polymer composition comprising a recurring    unit derived from an ester selected from (1) ethylenically    unsaturated organic esters of unsaturated C₃-C₂₀ monocarboxylic    acids and C₁ to C₂₄ monovalent aliphatic or alicyclic alcohols,    and (2) vinyl esters of saturated C₂-C₁₈ carboxylic acids, wherein    the ester content ranging from 2.5 to 8 wt %, preferably 3 to 6.5 wt    %, based on the total weight of the final ethylene polymer    composition; the ethylene polymer composition having a density    ranging from 0.92 to 0.94 g/mL, preferably 0.92 to less than 0.94,    g/mL, more preferably 0.92-0.935 g/mL; and-   II) 10 to 50%, preferably 10 to less than 50%, more preferably 20 to    35%, of an ethylene-based polymer component having a density ranging    from 0.9 to 0.930 g/mL, preferably 0.910 to 0.925 g/mL and a melt    flow rate up to 4 g/10 min, preferably from 0.5 to 2 g/10 min; the    said component being selected from:    -   i) a linear polyethylene (i) consisting of ethylene and 0.5 to        20% by mole of a CH₂═CHR α-olefin, where R is a hydrocarbon        radical having 2-8 carbon atoms; and    -   ii) a polymer blend (ii) comprising (a) 80-100 parts by weight        of a random interpolymer of ethylene with at least one CH₂═CHR        α-olefins, where R is a hydrocarbon radical having 1-10 carbon        atoms, the said polymer containing up to 20 mol % of CH₂═CHR        α-olefin and having a density between 0.88 and 0.945 g/mL;        and (b) from 5 to 30 parts by weight of a random interpolymer of        propylene with at least one CH₂═CHR α-olefin, where R is a        hydrocarbon radical having from 2 to 10 carbon atoms, and        possibly with ethylene, said interpolymer (b) containing from 60        to 98% by weight of units derived from propylene, from 2 to 40%        by weight of recurring units derived from the CH₂═CHR α-olefin,        and from 0 to 10% by weight of recurring units derived from        ethylene, and having a xylene-insoluble fraction a room        temperature greater than 70%.

The stretchable wrap film according to the present invention has a ratiobetween the value of MD tear resistance and the value of TD tearresistance over 0.3 and a value of MD tensile strength at 30% rangingbetween 6.5 to 15 N.

The film of the present invention has an improved balance of tearresistance measured in machine direction (MD) and transverse direction(TD). It means that the said two values of tear resistance are quitecloser to each other.

The preferred film has a ratio between the value of MD tear resistanceand the value of TD tear resistance over 0.35, in particular from 0.35to 1.5.

Preferably the film has a value of MD tensile strength at 30% rangingbetween 7 to 12 N, more preferably 7.5 to 12 N.

The preferred film has a value of MD normalised residual strength at 30%ranging from 6 to 9.5 cN/μm, preferably from 6.2 to 9.5 cN/μm.

The film advantageously has a ratio between the value of MD residualstrength at 30% and MD tensile strength at 30% over 0.46.

The preferred film of the present invention has a value of haze lessthan 16%.

The said mechanical and optical properties are determined as explainedhereinbelow.

As used herein, the phrase “normalised residual strength” is theresidual strength divided by the thickness of the film; the abbreviation“MD”means “machine direction”, and refers to a direction “along thelength” of the film, i.e., in the direction of the film as the film isformed during extrusion and/or coating; the abbreviation “ID” means“transverse direction”, and refers to a direction across the film,perpendicular to the machine or longitudinal direction.

Preferably, ethylene polymer composition (I) consist of an interpolymerof ethylene with at least one comonomer selected from above-mentionedesters (1) and (2), wherein the comonomer content is within the 2-8 wt %range.

The term “interpolymer” as used herein refers to polymers prepared bythe polymerization of at least two different types of monomers. Thegeneric term “interpolymer” thus includes the term “copolymers” (whichis usually employed to refer to polymers prepared from two differentmonomers) as well as the term “terpolymers” (which is usually employedto refer to polymers prepared from three different types of monomers,e.g., an ethylene/butene/hexene polymer).

Alternatively, ethylene polymer composition (I) can be a blendcomprising (a) an ethylene homopolymer or interpolymer of ethylene withat least one of above-mentioned esters (1) and (2) wherein the esterscontent is in an amount from 2 to less than 8 wt % and (b) aninterpolymer of ethylene with at least one of above-mentioned esters (1)and (2). In interpolymer (b) the content of the ester(s) can be higherthan 8 wt %, provided that in the blend the ester content is in therange from 2 to 8 wt %.

In said blend ethylene homopolymer (a) is preferably a low densityethylene homopolymer (which is known as LDPE), which typically has meltflow rate ranging from 0.1 to 20 g/10 min and a density value of0.915-0.932 g/mL. LDPE is produced according to known polymerisationmethod with a free radical initiator, such as peroxide and oxygen. It isgenerally produced by either a tubular or a stirred autoclave reactor.

In such a blend ethylene interpolymer (b) can have a density valuehigher than 0.940 g/ml.

As specific examples of the comonomers copolymerized with the ethylenemonomer to produce ethylene polymer composition (I), there can bementioned unsaturated carboxylic acid esters represented by acrylatesand methacrylates, which include acrylates and methacrylates having alinear or branched alkyl group with 1 to about 24 carbon atoms, such asmethyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate,t-butyl acrylate, isobutyl acrylate, pentyl acrylate, isononyl acrylate,hexyl acrylate, 2-methylpentyl acrylate, octyl acrylate, 2-ethylhexylacrylate, dodecyl acrylate, methyl methacrylate and ethyl methacrylate;lauryl(meth)acrylate and cyclohexyl(meth)acrylate.

In branched ethylene polymer composition (I) having low densitypreferred esters which can be copolymerized with ethylene include methylacrylate copolymers (EMA), ethyl acrylate (EEA copolymers), butylacrylate (EBA copolymers) and vinyl acetate (EVA copolymers). EMAcopolymers, EBA copolymers and EVA copolymers are the most preferredcopolymers.

Ethylene polymers (II) are inclusive of diverse groups of ethylenepolymers having low density. More specifically, the term “linearpolyethylene” used herein encompasses both heterogeneous materials aslinear low density polyethylene (LLDPE), very low and ultra low densitypolyethylene (VLDPE and ULDPE) as well as homogeneous polymers. Saidhomogenous polymers also known as plastomers are thermoplastichomopolymers of ethylene and interpolymers of ethylene, with one or moreα-olefins having 2-10 C-atoms, which are to be prepared by means ofmetallocene catalysts and other single-site catalysts. As a rule, theproportion of comonomer ranges between 0 and 50 wt. %, preferablybetween 5 and 35 wt. %. Said homogeneous polymers usually has a densitybetween 0.90-0.930 g/mL and a melt flow rate value of 0.8-2.0 g/10min at2.16 kg loading and 190° C. The homogeneous polymers are different fromthe polyethylenes prepared by means of Ziegler-Natta catalysts, forexample, in that they have a narrow molecular weight distribution, whichin terms of {overscore (M)}_(w)/{overscore (M)}_(n) values usuallyranges between 1.5 and 3, and a limited degree of long chain branching.As a rule, the number of long chains amounts to maximally 3 per 1000C-atoms.

Suitable homogeneous polymers are produced on a commercial scale, forexample by Exxon Chemical Company and DEX-Plastomers under the brandname Exact and by Dow Chemical Company, which commercializes them withthe trademark Engage, Affinity and Elite, and by Mitsui PetrochemicalCorporation, which commercialized them with the trademark Tafmer.

In ethylene polymer composition (I) the ester content is typically 3 toless than 5 wt % when ethylene-based polymer component (II) is ahomogeneous polymers.

Ethylene polymers (II) as interpolymers are obtained by copolymerizingethylene with the above CH₂═CHR α-olefins where R is a linear orbranched hydrocarbon radical with from 2 to 8 carbon atoms; the olefinis preferably selected from 1-butene, 1-hexene, 1-octene and4-methyl-1-pentene. The most preferable comonomers in the ethylenecopolymer are 1-butene, 1-hexene and 1-octene.

Linear polyethylene (II) used in the present invention is preparedaccording to known ways of polymerization involving the use ofcoordination catalysts of the “Ziegler-Natta” or “Philips” type. Forexample, it is prepared by copolymerization of ethylene with aC₄-C₁₀-α-olefin in the presence of a Ziegler-Natta type catalystobtained by the reaction of an organometallic compound of a metal fromgroups 2 and 3 of the Periodic Table with a catalytic componentcomprising a transition metal belonging to groups 4 to 6 of the PeriodicTable. Preferably the transition metal compound is supported on a solidcarrier comprising magnesium halide in active form. Examples ofcatalysts usable in the preparation of the copolymer are described inU.S. Pat. Nos. 4,218,339 and 4,472,520. The catalyst may also beprepared according to the methods described in the U.S. Pat. Nos.4,748,221 and 4,803,251. Particularly preferred are the catalystscomprising components having regular morphology, for example spherical.Examples of such catalysts are described in the European patentapplications 395083, 553805 and 553806.

The above polymer blend (ii) is described in international patentapplication WO 95/20009. The propylene polymer in blend (ii) may be, forexample, a copolymer of propylene with ethylene or a copolymer ofpropylene with butene-1. It is preferably a terpolymer of propylene withethylene and a C₄-C₁₀-α-olefin. In such a case, the propylene content isfrom 85 to 96 wt %, the ethylene content is from 2 to 8 wt % and theC₄-C₁₀-α-olefin content is from 2 to 7 wt %. In polymer blend (ii)component (a) is preferably a copolymer of ethylene with 1-butene andcomponent (b) is a terpolymer of propylene with ethylene and 1-butene.

The high insolubility in xylene of the propylene interpolymer (b) isindicative of a stereoregular structure of the propylene recurring unitsand of homogenous distribution of the comonomer(s) in the copolymerchain. The insolubility in xylene, determined as described hereinbelow,is preferably greater than 75 wt %, more preferably greater than 85 wt%.

The heat of fusion of the propylene interpolymer (b) is generallygreater than 50 J/g, preferably greater than 60 J/g, more preferablygreater than 70 J/g.

The melting temperature of the propylene interpolymer (b) is below 140°C. and preferably from 120° to 140° C.

The crystalline index of the propylene interpolymer (b) is generallygreater than 50%.

The MFR value, which is determined as described hereinbelow, of thepropylene interpolymer (b) is generally from 2 to 30 g/10 min.

The propylene interpolymer (b) can conveniently be prepared using ahighly stereospecific catalyst, for example, of the type described inpatent application EP 395 083.

Polymer blend (ii) can be obtained by firstly blending the components(a) and (b) in the solid state and then being fed into the extruderwherein the two components are mixed in the molten state, for example ina mixer with high mixing efficiency.

According to a preferred method, polymer blend (ii) is prepared directlyby polymerization process in at least two reactors in series which,working in any order and using the same catalyst in the variousreactors, ethylene polymer (a) is prepared in one reactor and thepropylene polymer (b) is produced in the other. The polymerization isconveniently carried out in the gas phase using fluidized-bed reactors.Examples of polymers prepared according to the said method are describedin patent applications WO 93/03078 and WO 95/20009. A suitable catalystis obtained from the reaction of:

-   A) a solid catalytic component comprising a titanium component    containing at least a titanium halogen bond supported on a magnesium    halide in active form and optionally an electron-donor compound;-   B) an Al-alkyl compound; and, optionally,-   C) an electron-donor compound.

The polymer blend according to the present invention is formed by anyconvenient method, including dry blending the individual components andsubsequently melt-mixing, either directly in the extruder used to makethe film, or by pre-melt mixing in separate extruder before making thefilm.

Obviously, in accordance with what is known by a person skilled in theart, further additives (such as stabilizers, antioxidant, antiblocking,slip agents, colours, etc.) and fillers than are capable of impartingspecific properties to the film of the present invention may be added tothe said polymer blend.

The film formed from the polymer blend described herein is made usingthe known film manufacturing method and equipment for blown films andcast films. For example, the blend may be cast into film with a flat dieor blown into film with a tubular die.

The film of the present invention may be monolayer or multilayer film.However, for coextruded multilayer film structures (e.g., 3-layer filmstructures) at least one skin layer should be made from the polymerblend described herein, of course it can also be used as a core layer ofthe structure. Generally, the polymer blend described herein comprisesat least 50% by weight of the total multilayer film structure.Preferably, the polymer blend disclosed herein is used as the corelayer. In such a film, the skin layers can comprise other polyethylenetypes from high to low density as well as polypropylene types, or blendsof them, in order to impart particular properties at inner or outer faceof the film.

A particular aspect of this invention can involve a multilayer filmwhere each layer of film consists of the same claimed polymercomposition which, however, contains different additives, stabilizers,fillers and so on.

The thickness of the film of the present invention may vary, but istypically from 25 to 100 μm, preferably from 40 to 70 μm. The filmtypically has a weight of from 25 to 90 g/m². For the three layer filmstructures same final thickness and weight are useful, but each layerdistribution may vary from 5 to 50% of the total film thickness, and anumber of layers are minimum 2 to 7, preferably 3 to 5.

The cast or blown film according to the present invention isparticularly suitable to be used for overlapping a plurality of items bythe method described in Italian patent No. 1285827, for example. In thecase of blown film, the process is carried out by using a blow-up ratio(known as B.U.R.) higher than 1.8. According to the said method the filmis formed into a tubular shape by sealing the two ends of the filmhaving a convenient length each other. Also, already formed tubularfilms are used then cut into the desired length, suitable for packagingstep. Then, the film is stretched with an appropriate mechanical deviceand a plurality of items is inserted inside the stretched tubular film.Finally, the mechanical device leaves again the film that closes theplurality of items thanks to elastic recovery of the film.

The films according to the present invention can be printable aftercorona treatment.

The following examples are given to illustrate and not to limit thepresent invention.

The data relating to the polymer blends and the films of the examplesare determined by way of the methods reported below.

-   MFR: Measured according to ISO method 1133 (190° C., 2.16 kg).-   Density: Measured according to ASTM method D-792.-   Comonomer content: Determined by IR spectroscopy, unless specified.-   Fractions soluble and insoluble in xylene at 25° C.: 2.5 g of    polymer are dissolved in 250 ml of xylene at 135° C. under    agitation. After 20 minutes the solution is allowed to cool to 25°    C., still under agitation, and then allowed to settle for 30    minutes. The precipitate is filtered with filter paper, the solution    evaporated in nitrogen flow, and the residue dried under vacuum at    80° C. until constant weight is reached. Thus one calculates the    percent by weight of polymer soluble and insoluble at room    temperature (25° C.).-   Tear resistance: Measured using an Elmendorf tear tester according    to ASTM method D 1922, determined both in machine direction and    transversal direction.-   2% secant tensile modulus: Determined according to ASTM method D    822.-   Tensile strength and residual strength: Determined according the MA    17301 internal method available upon request. A 12.7 mm×100 mm film    specimen is used.-   The test is carried out on a film specimen cut from a film. The film    has previously been kept at 23° C., 50% is the relative humidity,    for at least 24 hours but not over 48 hours.-   The film specimen is placed in an Instron-type dynamometer working    at a tensile rate of 50 mm/min. The film is stressed up to a    deformation of 30%. The strength is measured when the deformation of    30% is reached (maximum strength) and after 240 minutes from the    deformation of 30% is reached (strength 240). The residual strength    ratio is defined as the ratio between residual strength at strength    240 and maximum strength.-   Dart: Determined according to ASTM method D 1709A.-   Haze: Determined according to ASTM method D 1003.-   Packaging test: the films prepared as described in the examples are    used to wrap 6 bottles. The bottles are packed by using a packaging    machine described in Italian patent No. 1285827, the machine also    seals the two endings of the films.-   The evaluated properties are resistance of the sealed film portion    and quality of packaging.-   The quality of sealing is determined by evaluating resistance at    yielding or breakage of sealing portion after the sealing.-   The quality of packaging is determined by evaluating toughness of    the packaged items after 1 minute.

POLYMERS USED IN THE EXAMPLES AND COMPARATIVE EXAMPLES

-   Ethylene-butyl acrylate copolymer, EBA copolymer (1): the content of    recurring units derived from butyl acrylate is 4.5 wt %, the MFR    value is 0.25 g/10 min and the density is 0.922 g/mL;-   Ethylene-butyl acrylate copolymer, EBA copolymer (2): the content of    recurring units derived from butyl acrylate is 6.5 wt %, the MFR    value is 0.25 g/10 min and the density is 0.923g/mL;-   Ethylene-butyl acrylate copolymer, EBA copolymer (3): the content of    recurring units derived from butyl acrylate is 3.0 wt %, the MFR    value is 0.5 g/10 min and the density is 0.923 g/mL;-   Ethylene-vinyl acetate copolymer blend, EVA copolymer (1): it is a    blend made from 44 wt % of an ethylene-vinyl acetate copolymer    having a content of recurring units derived from vinyl acetate of 14    wt %, the MFR value is 0.3 g/10 min and the density is 0.938 g/mL    and 56 wt % of the low density ethylene homopolymer (LDPE) described    hereinbelow; the density of the blend is 0.930 g/mL;-   Ethylene-vinyl acetate copolymer, EVA copolymer (2): the content of    recurring, units derived from vinyl acetate is 5.0 wt %, the MFR    value is 0.5 g/10 min and the density is 0.928 g/mL;-   Ethylene-methyl acrylate copolymer blend, EMA copolymer: it is a    blend made from 25.3 wt % of ethylene-methyl acrylate copolymer    having a content of recurring units derived from methyl acrylate of    23.9 wt % (determined by ¹³C-NMR spectroscopy), the;MFR value is 2.4    g/10 min and the density is 0.946 g/mL and 74.7 wt % of the low    density ethylene homopolymer (LDPE) described hereinbelow, the    density of the blend is 0.928 g/mL;-   Ethylene-ethyl acrylate copolymer blend, EEA copolymer: it is a    blend made from 38.7 wt % of ethylene-ethyl acrylate copolymer    having a content of recurring units derived from ethyl acrylate of    16.5 wt % (determined by ¹³C-NMR spectroscopy), the MFR value is 1.1    g/10 min and the density is 0.929 g/mL and 61.3 wt % of the low    density ethylene homopolymer (LDPE) described hereinbelow, the    density of the blend is 0.925 g/mL;-   Low density polyethylene, LDPE: the ethylene homopolymer has an MFR    value of 0.3 g/10 min and density of 0.923 g/mL;-   Linear low density ethylene-octene-1 copolymer, LLDPE (1): the    content of recurring units derived from octene-1 is 10.0 wt % (2.71    mol %), MFR value is 2.5 g/10 min and the density is 0.919 g/mL;-   Linear low density ethylene-octene-1 copolymer, LLDPE (2): the    content of recurring units derived from octene-1 is 9.5 wt % (2.56    mol %), MFR value is 1 g/10 min and the density is 0.918 g/mL;-   Linear low density ethylene-hexene-1 copolymer, LLDPE (3): the    content of recurring units derived from hexene-1 is 12.1 wt % (4.39    mol %), MFR value is 2.3 g/10 min and the density is 0.917 g/mL;-   Very low density ethylene-octene-1 copolymer, VLDPE: the content of    recurring units derived from octene-1 is 15.3 wt % (4.3 mol %), MFR    value is 1 g/10 min and the density is 0.912 g/mL;-   Ethylene copolymer blend, LLDPE blend: it consists of (a) 85 wt % of    a terpolymer of ethylene and butene-1 and hexene-1 having 6.5 wt %    (3.45 mol %) of recurring units derived from butene-1 and 4 wt %    (1.42 mol %) of recurring units derived from hexene-1, the density    is 0.919 g/mL and (b) 15 wt % of terpolymer of propylene and    ethylene and butene-1, wherein the recurring units derived from    propylene, ethylene and butene-1 are 92.1, 2.3 and 5.6 wt %,    respectively, the density is 0.90 g/mL. The blend has an MFR value    of 0.7 g/10 min and density of 0.916 g/mL;-   Ethylene-hexene-1 copolymer, mPE (1): the content of recurring units    derived from hexene-1 is 7.0 w % (2.45 mol %), MFR value is 1 g/10    min and the density is 0.918 g/mL. The copolymer is prepared by    using a metallocene catalyst;-   Ethylene-hexene-1 copolymer, mPE (2): the content of recurring units    derived from hexene-1 is 3.9 wt % (1.33 mol %), MFR value is 0.7    g/10 min and the density is 0.927 g/mL. The copolymer is prepared by    using a metallocene catalyst.

Examples 1-14 and Comparative Examples 1-3

A polymer blend is produced by extruding the proper components in asingle screw type extruder (30 L/D screw length). Table 1 lists thepolymers used and their relative amounts. Then, the thus obtainedpolymer blends are filmed trough a 40 mm grooved feed single screwextruder (KRC40), thus single layer blown films are produced. The filmsaccording to the present invention are produced with a blow-up ratiohigher than 1.8, while the comparative films are produced with a blow-upratio less than or equal to 1.8.

The physical and mechanical properties of the films as well as theresults of the bundling test carried out on the films are reported inTable 2 and Table 3.

In comparison with the films of the comparative examples the filmsaccording to the present invention exhibit both a good balance ofmechanical properties, good transparency and good sealability.Resistance of the sealed film is an indirect index of the sealability ofthe film. The bundling test shows that the films according to thepresent invention only have those main properties that make a filmsuitable for bundling. TABLE 1 Comparative Components Examples Examples(wt %) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 1 2 3 EBA copolymer (1) 75 75 7575 0 0 0 0 0 0 0 0 75 0 0 0 0 EBA copolymer (2) 0 0 0 0 0 0 0 0 0 0 0 00 75 0 75 67 EBA copolymer (3) 0 0 0 0 0 0 75 75 0 0 0 0 0 0 0 0 0 EVAcopolymer (1) 0 0 0 0 75 0 0 0 75 0 0 0 0 0 0 0 0 EVA copolymer (2) 0 00 0 0 75 0 0 0 0 0 0 0 0 0 0 0 EMA copolymer 0 0 0 0 0 0 0 0 0 75 0 75 00 0 0 0 EEA copolymer 0 0 0 0 0 0 0 0 0 0 75 0 0 0 0 0 0 LDPE 0 0 0 0 00 0 0 0 0 0 0 0 0 100 0 0 LLDPE (1) 0 0 0 0 0 0 0 0 0 0 0 0 0 25 0 25 0LLDPE (2) 0 25 0 0 25 25 25 0 0 25 25 0 0 0 0 0 0 LLDPE (3) 0 0 0 0 0 00 0 0 0 0 0 25 0 0 0 0 VLDPE 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 33 LLDPEblend 25 0 0 0 0 0 0 25 25 0 0 25 0 0 0 0 0 mPE (1) 0 0 0 25 0 0 0 0 0 00 0 0 0 0 0 0 mPE (2) 0 0 25 0 0 0 0 0 0 0 0 0 0 0 0 0 0

TABLE 2 Examples Properties of the film 1 2 3 4 5 6 7 8 9 10 Averagethickness, 60 60 70 75 70 70 60 65 70 65 μm 2% secant MD 170 126 132 103122 118 125 126 117 124 tensile TD 201 142 162 110 131 123 127 133 123130 modulus, MPa MD Elmendorf tear 1.27 1.98 3.78 3.0 2.67 2.85 2.302.10 2.60 2.60 resistance, N MD/TD Elmendorf 0.41 0.37 0.51 0.54 0.500.57 0.50 0.37 0.48 0.39 tear resistance ratio MD tensile strength at11.0 9.2 9.7 8.8 11.4 10.0 9.9 9.4 10.2 8.2 30%¹⁾, N MD residualstrength 5.6 5.1 5.3 4.7 5.6 5.2 4.9 5.0 5.5 4.2 at 30%, N MD residualstrength 0.51 0.55 0.55 0.53 0.49 0.52 0.49 0.53 0.54 0.51 at 30%/MDtensile strength at 30% ratio MD 9.3 8.5 7.6 6.3 8.0 7.4 8.2 7.7 7.9 6.5normalized residual strength at 30%, cN/μm Dart, g 249 388 222 711 447364 400 426 526 368 Haze, % 15.5 12.5 12.4 12.3 8.4 9.5 9.8 9.3 8.0 12.9Comparative Examples Examples Properties of the film 11 12 13 14 1 2 3Average thickness, 65 65 70 65 85 50 65 μm 2% secant MD 120 131 119 105188 125 110 tensile TD 123 132 120 107 199 147 117 modulus, MPa MDElmendorf tear 2.70 3.10 3.28 2.97 2.80 1.27 1.98 resistance, N MD/TDElmendorf 0.41 0.51 0.63 0.52 0.23 0.28 0.17 tear resistance ratio MDtensile strength at 8.9 9.4 9.0 7.6 13.0 6.1 11.0 30%¹⁾, N MD residualstrength 4.5 4.6 4.5 4.0 5.9 3.4 6 at 30%, N MD residual strength 0.510.49 0.50 0.53 0.45 0.56 0.54 at 30%/MD tensile strength at 30% ratio MD6.9 7.1 6.4 6.2 6.9 6.8 9.2 normalized residual strength at 30%, cN/μmDart, g 345 407 459 435 162 209 570 Haze, % 12.6 14.2 17.7 16.8 17 10 17¹⁾Force required to cause the stretching of 30% of a specimen ofmaterial.

TABLE 3 Bundling test Examples Properties of the film 1 2 3 4 5 6 7 8 910 Resistance of sealed good good very very good good good good goodgood film portion good good Toughness of packaged very good good goodgood good excellent good excellent excellent items after 1 minute goodComparative Examples Examples Properties of the film 11 12 13 14 1 2 3Resistance of sealed good good good good poor good good film portionToughness of packaged very excellent good good good bad bad items after1 minute good

1. A stretchable wrap film having a value of MD tear resistance, a valueof TD tear resistance, and a value of MD tensile strength at 30%comprising a polymer blend, the polymer blend comprising (percent byweight): I) 50 to 90% of an ethylene polymer composition having an estercontent, comprising a recurring unit derived from an ester selected from(1) ethylenically unsaturated organic monomer of esters of unsaturatedC₃-C₂₀ monocarboxylic acids and C₁ to C₂₄ monovalent aliphatic oralicyclic alcohols, and (2) vinyl esters of saturated C₂-C₁₈ carboxylicacids, wherein the ester content ranges from 2.5 to 8 wt % based on thetotal weight of the ethylene polymer composition; the ethylene polymercomposition having a density ranging from 0.920 to 0.94 g/mL; and II) 10to 50% of an ethylene-based polymer component having a density rangingfrom 0.9 to 0.930 g/mL and a melt flow rate up to 4 g/10 min; theethylene-based polymer component being selected from: i) a linearpolyethylene consisting of ethylene and 0.5 to 20% by mole of a firstCH₂═CHR α-olefin, where R is a hydrocarbon radical having 2-8 carbonatoms; and ii) a polymer blend comprising (a) 80-100 parts by weight ofa random polymer of ethylene with at least one second CH₂═CHR α-olefin,where R is a hydrocarbon radical having 1-10 carbon atoms, the randompolymer (a containing up to 20 mol % of the second CH₂═CHR α-olefin andhaving a density between 0.88 and 0.945 g/mL; and (b) from 5 to 30 partsby weight of a random interpolymer of propylene with at least one thirdCH₂═CHR α-olefin, where R is a hydrocarbon radical having from 2 to 10carbon atoms, and optionally with ethylene, said random interpolymer (b)containing from 60 to 98% by weight of units derived from propylene,from 2 to 40% by weight of recurring units derived from the thirdCH₂═CHR α-olefin, and from 0 to 10% by weight of recurring units derivedfrom ethylene, and having a xylene-insoluble fraction a room temperaturegreater than 70%; wherein the stretchable wrap film has a ratio betweenthe value of MD tear resistance and the value of TD tear resistance over0.3 and the value of MD tensile strength at 30% ranges between 6.5 to 15N.
 2. The film of claim 1, wherein polymer composition (I) is selectedfrom ethylene-methyl acrylate copolymer, ethylene-ethyl acrylatecopolymer, ethylene-butyl acrylate copolymer and ethylene-vinyl acetatecopolymer.
 3. The film of claim 1, wherein in linear polyethylene (i),the first CH₂═CHR α-olefin is selected from butene-1, hexene-1, octene-1and 4-methyl-1-pentene.
 4. The film of claim 1, wherein in polymer blend(ii), the random polymer (a) is an ethylene-butene-1 copolymer.
 5. Thefilm of claim 1, wherein in polymer blend (ii), the random interpolymer(b) is a propylene-ethylene-butene-1 terpolymer.
 6. A containerpackaging comprising a stretchable wrap film having a value of MD tearresistance, a value of TD tear resistance and a value of MD tensilestrength at 30% comprising a polymer blend, the polymer blend comprising(percent by weight): I) 50 to 90% of an ethylene polymer compositionhaving an ester content, comprising a recurring unit derived from anester selected from (1) ethylenically unsaturated organic monomer ofesters of unsaturated C₃-C₂₀ monocarboxylic acids and C₁ to C ₂₄monovalent aliphatic or alicyclic alcohols, and (2) vinyl esters ofsaturated C₂-C₁₈ carboxylic acids, wherein the ester content ranges from2.5 to 8 wt % based on the total weight of the ethylene polymercomposition, the ethylene polymer composition having a density rangingfrom 0.920 to 0.94 g/mL: and II) 10 to 50% of an ethylene-based polymercomponent having a density ranging from 0.9 to 0.930 g/mL and a meltflow rate up to 4 g/10 min; the ethylene-based polymer component beingselected from: i) a linear polyethylene consisting of ethylene and 0.5to 20% by mole of a first CH₂═CHR α-olefin, where R is a hydrocarbonradical having 2-8 carbon atoms: and ii) a polymer blend comprising (a)80-100 parts by weight of a random polymer of ethylene with at least onesecond CH₂═CHR α-olefin, where R is a hydrocarbon radical having 1-10carbon atoms, the random polymer (a) containing up to 20 mol % of thesecond CH₂═CHR α-olefin and having a density between 0.88 and 0.945g/mL; and (b) from 5 to 30 parts by weight of a random interpolymer ofpropylene with at least one third CH₂═CHR α-olefin, where R is ahydrocarbon radical having from 2 to 10 carbon atoms, and optionallywith ethylene, said random interpolymer (b) containing from 60 to 98% byweight of units derived from propylene, from 2 to 40% by weight ofrecurring units derived from the third CH₂═CHR α-olefin, and from 0 to10% by weight of recurring units derived from ethylene, and having axylene-insoluble fraction a room temperature greater than 70%: whereinthe stretchable wrap film has a ratio between the value of MD tearresistance and the value of TD tear resistance over 0.3 and the value ofMD tensile strength at 30% ranges between 6.5 to 15 N.